The present invention generally relates to environmental control systems (ECSs) and air cycle cooling systems (ACCSs). More specifically, the present invention relates to an improved ACCS and improved method of conditioning water vapor bearing compressed air and recovering wasted energy from a liquid load, while reducing the system size and bleed air consumption, and improving water removal efficiency.
ACCSs are used to provide a supply of conditioned air to an enclosure, such as an aircraft cabin and cockpit. In the past, ACCSs have utilized an air-to-air cycle cooling system with an integrated liquid loop. But the liquid loop has been primarily for the purpose of cooling radar or other avionics, not for cooling the air to be conditioned. In such systems, a flow of bleed air is taken from an intermediate or high pressure stage within a jet engine having multi-compression stages. The bleed air has usually been pre-cooled within a primary heat exchanger with heat being rejected to RAM air and then flowed to a compressor. After compression, the air has been routed through a second heat exchanger. Next, the air is typically flowed into an air-to-air reheater heat exchanger and then to an air-to-air condenser heat exchanger. Condensed water vapor is extracted by a water extractor, and then routed and evaporated in the second heat exchanger. A dehumidified air moves from the second heat exchanger to the reheater and into a turbine. An expanded air from the turbine flows through the condenser in the capacity as a coolant medium. When the air flow from the condenser passes through a liquid-to-air heat exchanger, a relatively warmer liquid from a liquid loop is cooled and then used to cool avionics. After the air flow moves through the liquid-to-air heat exchanger, the flow becomes the supply to the cabin.
Although providing advantages, the above conventional ACCS with a liquid loop has also presented disadvantages. For example, the liquid load is typically rejected directly into the cooling air supply. When the liquid load is high, it usually warms the air beyond the desired supply temperature. That means the ACCS will have to be increased in size to accommodate the load. The need for both a condenser and reheater adds bulk to the system. Of course, with fewer components, greater cooling capacity can be achieved with a given amount of space. If the ACCS is used as a retrofit, a bulkier system size means fewer opportunities for the ACCS to fit into different spaces to be retrofitted.
In a specific example of an air cycle system with a liquid cooling loop, U.S. Pat. No. 4,430,867 moves a compressed bleed air moves into a liquid/air condenser. From the liquid/air condenser, the air moves through a water collector and then directly to a turbine. Accordingly, the air into the turbine has not been reheated. From the turbine, an expanded air passes through a first liquid/air heat sink exchanger and then into a cabin. In the liquid loop, a heated liquid moves from the liquid/air condenser for use as ice melting at the upstream face of the first liquid/air heat sink exchanger. The liquid then moves through a second liquid/air heat sink exchanger inside a cabin and back to the liquid/air condenser. Accordingly, the liquid from a liquid load (i.e., the second liquid/air heat sink exchanger) is being used to condense and remove water at the turbine inlet. What is evidently not addressed, at least explicitly, is the problem of recovering heat rejected by the liquid loop.
U.S. Pat. No. 5,906,111 is assigned to the same assignee as the present invention and provides an air cycle subsystem and liquid cycle subsystem. The air cycle provides a compressed air to a liquid-to-air condenser and then a water extractor. A dehumidified air from the water extractor moves into a liquid-to-air reheater, a turbine, and then into first and second liquid-to-air heat exchangers. The air from the second liquid-to-air heat exchanger is used to cool an enclosure. The liquid cycle flows liquid through the first liquid-to-air heat exchanger, the condenser, the reheater, and then the second liquid-to-air heat exchanger. Thereby, the liquid cycle assists in removing water from the air in the air cycle. Although part of the wasted energy from the liquid load is recovered, a higher efficiency might still be achieved.
A variation of the air cycle system shown in U.S. Pat. No. 4,430,867 is U.S. Pat. No. 5,086,622, both of which are by the same inventor. In the latter, bleed air is compressed in a compressor and then flowed to an air-to-air condenser. Upon water vapor being condensed and then extracted, a dehumidified air moves to a first turbine for expansion. A discharge air from the first turbine moves back to the condenser and then to a second turbine. From the second turbine, the air can be supplied to a cabin. In this design, a dehumidified air does not flow through a reheater prior to entering the first turbine. That presents at least one disadvantage since the residual condensed water droplets in the first turbine inlet stream impinge on cold turbine blades and outlet walls and freeze out if the metal temperatures are much below freezing. Ice then quickly accumulates and must be rapidly melted to avoid clogging.
In the air cycle system shown in European Patent no. 248,578 B1, a compressor compresses an air flow which then moves through a coolant heat exchanger. The air then passes through a first turbine and into a first load heat exchanger. Thereafter, the air is ducted into a second turbine and then to a second load heat exchanger. The first and second load heat exchangers heat exchange with heat loads and are cooled by air or other mediums. Omitted from the disclosure, however, is if and how water is extracted from the air. Also omitted is how the loads can be balanced between the two stage turbines such that a practical design can be achieved.
As can be seen, there is a need for an ACCS with a liquid loop that is small in size such that for a given space a greater cooling capacity can be achieved. There is also a need for an ACCS which, due to its relatively small size, can serve as a retrofit in more environments. Further, an ACCS is needed which can more efficiently utilize the bleed air as a cooling medium. Also needed is an environmental control system that allows an ACCS to recover wasted thermal energy from a liquid cycle system. Still another need is for an ACCS that can recover a heat of condensation and sensible cooling.